Acanthamoebic keratitis is an infection of the cornea that is sight threatening. The infective organisms are widely distributed in the United States environment, but are relatively ineffective pathogens. Unlike disseminated Acanthamoeba infections, which are life threatening and occur in patients with compromised immune systems, acanthamoebic keratitis patients appear to be otherwise healthy. Contact lenses appear to increase the probability of contracting the infection. Existing treatment is not sufficiently effective. Even in those cases successfully treated, the disease course is excessively prolonged and involves much pain and loss of vision. This research will investigate the characteristic of Acanthamoeba that appears to determine its opportunistic pathogen property with the aim of developing new therapies. The life cycle of Acanthamoeba, like many important pathogens, includes a dormant form. The putative receptors with which spores and cysts must maintain communication with the extracellular environment are natural focus points for disease prophylaxis and treatment. Yet, except for what is described here, no other receptor of this type has been identified, even from the most studied systems, bacterial spore germination. They have identified a receptor, ESP, which controls absolutely the encystment and excystment of Acanthamoeba castellanii and, consequently, cell division. They also possess four monoclonal antibodies, which react with different epitopes of ESP. Synergy experimentation suggests that ESP is an osmolarity monitor. Anti-ESP bivalent antibodies mimic the natural stimulus for differentiation, causing the organism to cease dividing. The latter characteristic is apparently why Acanthamoeba are poor pathogens. Exploiting this circumstance should easily provide quick and effective therapies for Acanthamoeba pathologies. Experiments will be prepared to extend the ESP/osmolarity receptor results to acanthamoebic keratitis pathogens. They will isolate and sequence the ESP gene from Acanthamoeba castellanii. With polynucleotide probes prepared using the latter information, they will first identify, then isolate, sequence, and employ the homologous genes from pathogenic strains of Acanthamoeba to obtain reasonable quantities of ESP homologs. These proteins, anti-ESP antibodies, and should it prove advantageous, portions of the cDNA, will be used to confer therapeutic immunity. The therapeutic testing will employ the excellent animal models of acanthamoebic keratitis at the University of Texas Southwestern Medical Center, Dallas and the in vivo experiments will be done there.